1. Field of the Invention
The present invention relates to a surface acoustic wave device for use as a resonator and a band filter, and more particularly, the present invention relates to an edge reflection type surface acoustic wave device which utilizes Shear Horizontal (SH) type surface acoustic wave.
2. Description of the Related Art
Edge reflection type surface acoustic wave devices which utilize SH type surface acoustic waves such as BGS (Bleustein-Gulyaev-Shimizu wave) waves, Love waves, leaky waves and other such surface acoustic waves are known. In an edge reflection type surface acoustic wave device, a surface acoustic wave is reflected between a pair of opposite edges of a surface acoustic wave substrate. Therefore, it is not necessary to provide reflectors at both ends of the surface acoustic wave substrate or on both sides in the surface acoustic wave propagation direction of the area in which interdigital transducers are located. Accordingly, a surface acoustic wave device having a reduced size can be provided.
In an edge surface acoustic wave device including a surface acoustic wave substrate made of a piezoelectric single crystal, an unnecessary wave, such as a bulk wave or other undesirable wave, propagating from the surface of the substrate to the inner portion thereof and excited simultaneously with an SH type surface acoustic wave is reflected between the edges of the surface acoustic wave substrate and causes a large ripple to be generated in an attenuation frequency characteristic. For example, a large ripple tends to occur in the top thereof, that is, in the pass band.